I also looked at my bland purple Google forms and decided to use the header to incorporate images from the Spanish-speaking world. So I went to Pixabay and grabbed some (free public domain!) images of different places in the Spanish-speaking world and started making my forms more visually appealing. Google also pulls colors out of your picture to make possible palettes to use as your background colors, so you don't need to have any sense of coordinating colors to make a reasonably attractive form (which is great for me, because although I keep trying to do this, I have no sense of color combinations and it always ends badly).
|Sad, boring Google form
|Google form that reminds me of my trip to Puerto Rico